Hydraulic pumps are used in a number of systems. In many designs, an electric motor is used to turn a rotor that receives fluid from an inlet, applies pressure to the fluid, and discharges the pressurised fluid through an outlet. A known design of hydraulic pump is a vane pump in which rotating vanes trap a portion of fluid and entrain the fluid past a cam surface on the stator, the cam surface acting to reduce the volume of the chamber as the vanes rotate, thus applying pressure to the fluid before the fluid is discharged through an outlet.
While various designs of hydraulic pump exist, there is a drive to reduce the complexity and manufacturing difficulty of hydraulic pumps, to meet the requirements of efficiency, flow-rate, weight, complexity of manufacture and maintenance, and cost.